UNIVERSITY   OF  CALIFORNIA    AGRICULTURAL   EXPERIMENT    STATION 

*»«.■  •   e-^.1-     *%•-     .ABi^iii  viicm-  BENJ.    IDE    WHEELER,    President 

COLLEGE   OF  AGRICULTURE 

THOMAS    FORSYTH    HUNT,    DEAN    AND    Director 

BERKELEY  H-  E-   VAN   norman,  vice-director  and  dean 

University    Farm    School 


CIRCULAR  No.  156 
October,  1916 

HOW  TO  OPERATE  AN  INCUBATOR 

By  J.  E.  DOUGHERTY 


Getting  Ready. — Before  the  beginning  of  the  hatching  season  each 
year,  the  incubator  equipment  should  be  carefully  gone  over.  Each 
incubator  should  be  overhauled  to  see  that  all  mechanical  parts  are 
in  good  order  and  working  freely.  One  or  two  extra  thermometers 
and  a  few  wicks  should  always  be  kept  on  hand. 

Locating  the  Incubator. — Place  the  machine  in  a  room  where  the 
temperature  remains  fairly  uniform  at  all  times  and  where  there  is 
plenty  of  ventilation  without  drafts.  A  cellar  is  usually  best  because 
it  is  well  protected  from  the  direct  rays  of  the  sun  and  the  tempera- 
ture is  uniformly  low.  A  good  temperature  for  an  incubator  room  is 
60  degrees  F.  In  this  climate  good  ventilation  is  easily  secured  by 
removing  the  windows  wholly  or  in  part  and  inserting  in  their  places 
frames  covered  with  light  muslin.  The  air  will  pass  through  the 
muslin  but  the  wind  will  be  shut  out. 

Having  located  the  incubator,  level  it  with  a  spirit  level.  Leveling 
is  very  important,  for  if  the  machine  is  not  level,  one  part  of  the 
egg  tray  will  be  higher  than  another,  and  the  eggs  in  that  part  will 
therefore  obtain  more  heat  than  the  others. 

Disinfection. — Before  and  after  every  hatch,  the  incubator  should 
be  thoroughly  washed  and  sprayed  and  the  movable  parts  placed  in 
the  sun  to  dry.  Thoroughly  cleanse  every  part  with  soap,  water  and 
a  good  scrubbing  brush.  A  few  hours  before  putting  in  the  eggs 
spray  all  parts  of  the  interior  of  the  incubator  with  a  spray  pump, 
using  about  a  2  per  cent  solution  of  some  good  disinfectant,  such  as 
cresol  compound  or  any  of  the  "eum"  preparations.  The  fumes  of 
the  disinfectant  will  penetrate  every  crack  in  the  hot  interior  of  the 
egg  chamber  and  the  vapors  remaining  when  the  eggs  are  put  in 
will,  to  some  extent,  disinfect  the  exterior  of  the  eggs.  To  disinfect 
thoroughly  the  surfaces  of  the  eggs,  dip  them  fairly  rapidly  in  95  per 
cent  pure  alcohol  just  before  putting  them  into  the  incubator.     This 


is  an  advisable  precautionary  measure  because  certain  very  contagious 
diseases  are  believed  to  be  transmitted  from  adult  stock  to  newly 
hatched  chicks  by  means  of  infection  of  the  surface  of  the  shell. 
Coccidiosus  is  one  of  these  diseases. 

The  Lamp. — The  lamp  should  be  thoroughly  cleaned,  the  burner 
boiled  in  a  solution  of  washing  soda  and  a  new  wick  put  in,  if  neces- 
sary, before  the  machine  is  started  every  season. 

In  beginning  the  hatch,  use  a  medium  name,  and  adjust  the  thermo- 
stat to  it.    If  too  small  a  flame  is  used  to  start  with,  the  flame  cannot 


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Fig.  1. — Cross-section  of  a  hot-air  heated  incubator  showing  the  method  of 
regulating  the  temperature,  the  ventilation  system,  and  the  general  construction. 
°  (a)  Counterpoise  weight;  (ft)  regulator  arm;  (c)  connecting  rod;  (d)  thumb 
nut;  (e)  pivot  casting;  (f)  heater  disc;  (g)  c6tton  batting  filling  between  inside 
and  outside  cases;  (h)  thermostat;  (t)  egg  chamber;  (j)  moisture  pan  filled  with 
sand  kept  wet;  (fc)  nursery;  (w)  bottom  ventilator  for  escape  of  air  from  egg 
chamber;  (w)  insulation  in  bottom  of  incubator;  (p)  one  of  four  pipes  to  discharge 
air  from  above  level  of  eggs  into  false  bottom  beneath  egg  chamber;  (r)  fresh 
air  intake;   (s)  outlet  for  escape  of  lamp  fumes.     No  fumes  can  get  into  machine. 


be  turned  low  enough  at  the  end  of  the  hatch,  in  warm  weather,  to 
keep  the  temperature  from  running  up.  If  too  high  a  flame  is  used 
the  lamp  will  smoke. 

The  lamp  should  be  cleaned  and  filled  every  morning  after  turn- 
ing the  eggs.  If  filled  before  turning  the  eggs,  the  hands,  being 
smeared  with  oil  from  the  lamp,  will  leave  a  coating  of  oil  on  the 
eggs  and  cause  serious  injury  to  the  growing  embryos.  Trim  the 
wick  with  a  burnt  match  or  cloth  by  simply  rubbing  off  the  charred 
crust  and  then  wipe  away  all  dirt  and  oil  from  all  parts  of  the  lamp 


before  replacing  in  the  incubator.  In  trimming,  cover  the  end  of  the 
finger  with  a  cloth  and  turn  the  wick  just  high  enough  to  expose 
the  charred  part  above  the  top  edge  of  wick  tube.  Rub  off  the  charred 
crust  by  rubbing  in  one  direction  only;  this  causes  all  the  threads  of 
the  wick  to  lie  smoothly  in  one  direction  and  results  in  a  more  even 
flame.  Then  turn  the  wick  up  about  one-sixteenth  of  an  inch  and 
pat  down  the  corners  lightly  to  prevent  high  corners  on  the  flame, 
which  would  cause  smoking.  A  flame  that  is  straight  across  the  top 
and  rounded  at  the  corners  gives  the  most  heat  and  will  not  smoke. 

Thermometer. — In  order  to  be  certain  that  the  thermometer  is  cor- 
rect, the  operator  should  test  it  himself  with  a  clinical  thermometer. 
Place  both  thermometers  in  luke-warm  water  and  while  stirring,  add 
hot  water  slowly  until  the  clinical  thermometer  registers  103  degrees. 
Observe  whether  the  incubator  thermometer  gives  a  similar  reading. 
If  not,  the  operator  knows  that  at  103  degrees  the  incubator  ther- 
mometer reads,  perhaps,  102%  degrees,  and  he  must  allow  for  this 
error  in  running  his  incubator.  Faulty  thermometers  have  caused 
more  damage  in  the  way  of  poor  hatches  than  is  generally  realized. 

Temperature. — In  all  incubators  the  temperature  is  regulated  or 
controlled  by  a  thermostat.  The  all-metal  thermostat  (see  Fig.  2) 
consists  of  three  pieces  of  metal  riveted  together  at  the  ends  and  is 
designed  on  the  principle  that  different  metals  expand  different  definite 
amounts  for  every  degree  F.  rise  in  temperature  and  contract  the  same 
amounts  for  every  degree  F.  fall  in  temperature.  The  central  piece 
of  metal  (h,  Fig.  2)  does  not  expand  or  contract  as  much  for  every 
degree  of  change  in  temperature  as  do  the  two  outside  pieces.  As  a 
result,  since  all  three  pieces  are  riveted  at  the  ends,  the  two  outside 
pieces,  expanding  more  rapidly  than  the  central  piece,  are  forced  out- 
ward in  the  middle  when  the  temperature  rises.  This  buckling  or 
spreading  apart  of  the  two  outside  pieces  of  metal  in  the  thermostat 
causes  a  downward  pull  on  the  connecting  rod  (c),  which  in  turn 
pulls  on  the  lever  arm  (b)  and  raises  the  disc  (/)  off  the  heater. 

When  the  temperature  in  the  incubator  rises  above  the  desired 
temperature,  the  expansion  of  the  thermostat  lifts  the  disc  from  one- 
half  inch  to  one  and  one-half  inches  above  the  heater,  allowing  the 
surplus  heat  to  escape.  But  just  as  soon  as  the  temperature  returns 
to  its  proper  place,  the  disc  lowers  again.  If  the  temperature  of  the 
machine  should  drop  below  the  "running"  temperature,  the  thermo- 
stat will  contract  and  allow  the  disc  to  settle  down  on  the  heater,  thus 
tightly  closing  the  opening  and  forcing  all  the  heat  into  the  egg 
chamber.    When  the  temperature  is  properly  regulated,  the  disc  should 


stand  about  one-sixteenth  to  one-eighth  inch  above  the  opening  in  the 
top  of  the  heater.  There  are  a  number  of  different  kinds  of  thermo- 
stats or  heat-regulating  devices  used  on  different  makes  of  machines, 
but  they  are  all  based  on  the  principle  of  expansion  and  contraction 
of  a  thermostatic  device  within  the  egg  chamber  to  control  the  amount 
of  heat  entering,  and  thus  automatically  regulating  the  temperature 
of  the  egg  chamber. 

In  the  type  of  heater  shown  in  Fig.  2,  the  fumes  from  the  lamp 
cannot  get  into  the  egg  chamber,  but  must  escape  through  the  opening 
(s).  The  fresh  air  (as  shown  by  arrows)  is  heated  by  the  lamp  as  it 
is  drawn  into  the  opening  (r).  It  passes  into  the  top  of  the  incubator 
and  then  diffuses  through  a  burlap  or  muslin  diaphragm  into  the  egg- 
chamber.  After  circulating  around  the  eggs,  absorbing  the  carbon 
dioxide  thrown  off  by  the  eggs  and  giving  up  oxygen,  the  air  current 
passes  through  the  openings  at  the  sides  of  the  egg  chamber  and 
escapes  through  the  bottom  of  the  machine. 

The  temperature  throughout  the  hatch  should  be  102  degrees  when 
the  center  of  the  thermometer  bulb  is  on  a  level  with  the  tops  of  the 
eggs.  Hanging  thermometers  having  the  center  of  the  thermometer 
bulb  above  the  tops  of  the  eggs  need  to  be  run  higher  according  to  the 
height  of  bulb  above  egg,  because  the  heat  in  nearly  all  incubators 
comes  into  the  egg  chamber  from  the  top  and  the  nearer  the  ther- 
mometer is  to  the  top  of  the  egg  chamber  the  higher  it  will  read,  when 
a  standing  thermometer  on  a  level  with  the  tops  of  the  eggs  registers 
102  degrees  F.  While  chicks  are  hatching  the  temperature  can,  and 
often  does,  run  up  to  104  degrees  without  doing  any  harm. 

Ventilation. — Good  ventilation  of  the  egg  chamber  is  a  very  im- 
portant part  of  the  process  of  incubation.  During  the  growth  of  the 
embryo,  it  has  for  its  food  supply  the  stored-up  food  within  the  egg. 
In  order  to  utilize  this  stored-up  food  and  transform  it  into  new  body 
tissue,  heat,  and  muscular  action  (such  as  the  pumping  of  the  blood 
through  the  blood  vessels  that  radiate  through  all  parts  of  the  develop- 
ing eggs),  oxygen  is  absolutely  necessary.  Without  oxygen,  growth 
could  not  go  on  and  the  embryo  would  die.  The  net-work  of  blood 
vessels  which  extend  in  great  numbers  close  to  the  underside  of  the 
shell  and  to  the  air-cell,  take  up  oxygen  from  the  incoming  fresh  air 
and  throw  off  carbon  dioxide,  which  has  been  given  off  as  a  waste 
product  by  the  growing  body  tissues.  Therefore,  plenty  of  fresh  air 
is  essential  to  the  production  of  strong,  vigorous  chicks.  Briefly  stated, 
the  developing  embryo  breathes  in  fresh  air  through  the  pores  of 
the  shell  and  from  the  air  cell.    It  exhales  poisonous  carbon  dioxide 


through  the  pores  of  the  shell  and  into  the  air  cell.  The  ventilation 
of  the  incubator  should  be  such  as  to  carry  fresh  air  into  the  egg 
chamber  as  rapidly  as  it  is  needed  and  to  carry  away  the  carbon 
dioxide  as  rapidly  as  it  is  given  off  by  the  eggs.  Insufficient  ventila- 
tion will  rob  the  chicks  of  vitality  even  though  it  may  not  prevent 
hatching. 

Insufficient  ventilation  in  the  egg  chamber  which  is  not  always 
readily  detected  during  the  first  nineteen  days  of  the  hatch  will  reveal 
itself  after  a  good  many  of  the  chicks  have  hatched  out.  The  panting 
of  the  chicks  after  hatching  is  invariably  caused  by  too  little  ventila- 
tion, rather  than  by  too  much  heat.  Even  though  the  hatch  is  not 
over,  more  ventilation  must  be  given  if  the  chicks  already  hatched  are 
not  to  be  weakened. 

Moisture. — The  process  of  exhaling  in  the  developing  egg  is  closely 
analogous  to  that  in  human  beings.  The  exhaled  air  is  laden  with 
moisture,  and  it  is  as  a  result  of  giving  off  used  moisture  in  this  way 
that  the  eggs  "dry  down"  during  embryonic  growth.  This  drying 
down  causes  a  gradual  loss  of  the  water  content  of  the  egg  and  a  cor- 
respondingly gradual  increase  in  the  size  of  the  air  cell.  When  the 
air  passing  through  the  egg  chamber  is  very  dry  it  not  only  takes  up 
and  carries  off  the  moisture  naturally  exhaled  by  the  egg,  but  also 
passes  through  the  porous  shell  and  absorbs  still  more  moisture.  It 
is  because  of  this  excessive  drying  down  of  the  egg  that  the  embryo 
is  injured.  Nature  supplies  the  egg  with  just  enough  water  to  enable  it 
to  carry  on  its  life  processes  and  to  evaporate  gradually  by  the  process 
of  exhalation.  From  this  we  can  clearly  understand  the  vital  necessity 
of  having  the  air  passing  through  the  egg  chamber  sufficiently  sat- 
urated with  moisture  to  prevent  undue  evaporation  of  the  moisture 
from  the  egg.  Sixty  per  cent  humidity  is  generally  considered 
adequate. 

It  is  evident  that  ventilation  and  moisture  conditions  are  closely 
related  and  cannot  be  considered  as  separate  problems.  They  must  be 
handled  together.  Geographical  location,  time  of  year,  and  other 
factors  will  have  to  determine  whether  artificial  means  of  adding 
moisture  to  the  air  entering  the  egg  chamber  is  necessary  or  not.  In 
the  better  types  of  incubators,  ventilation  is  very  well  taken  care  of, 
so  that  the  chief  problem  to  consider  is  the  maintenance  of  sufficient 
moisture  in  the  circulating  air.  Always  follow  the  instructions  sent 
out  by  the  incubator  manufacturer  in  this  regard  until  sufficient  experi- 
ence has  been  gained  to  enable  one  to  act  intelligently  in  making  any 
change  that  may  appear  advisable.    The  increase  in  size  of  the  air-cell, 


6 

the  drying  of  the  membrane  exposed  when  the  chick  pips  the  shell, 
the  collection  of  moisture  on  the  inside  of  the  glass  of  the  incubator 
door  (see  following  page),  and  the  ease  with  which  the  chicks  break 
from  the  shell,  together  with  experience,  will  serve  as  definite  guides 
in  properly  regulating  moisture  conditions  and  ventilation  in  artificial 
hatching. 

During  the  hatching  period,  frequent  observations  of  the  air-cells 
will  indicate  the  rate  of  evaporation  of  the  egg  and  if  too  much  or 
too  little  moisture  is  being  supplied.  Experience  will  soon  teach  one 
the  proper  rate  of  evaporation  as  shown  by  a  gradual  increase  in  the 


-  -    Fresh  Egg 

7th  day 

---   14th  day 

-  ~    19th  day 


Fig  2. — Showing  gradual  increase  in  size  of  air-cell  due  to  evaporation  of 
water  during  the  period  of  incubation. 

size  of  the  air-cell.  A  good  plan  for  the  beginner  is  for  him  to  set 
a  hen  on  the  ground  in  an  out-door  setting  coop  at  the  same  time  that 
he  sets  the  incubator  and  compare  the  increase  in  size  of  the  air-cells 
in  both  cases  every  few  days. 

After  the  chicks  have  begun  to  hatch,  a  light  film  of  moisture  or 
a  few  beads  of  water  should  appear  along  the  lower  inside  edge  of 
the  glass  of  the  incubator  door.  Only  a  little  moisture  should  collect 
on  the  inside  of  glass  door.  Too  much  humidity  in  the  egg  chamber 
is  indicated  at  this  time  by  too  great  a  collection  of  moisture  on  the 
glass  and  can  be  corrected  by  increasing  the  ventilation  or  by  reducing 
the  moisture  supplied.  Too  little  humidity  is  indicated  by  no  moisture 
on  the  inside  of  the  glass  door,  and  by  the  rapid  drying  and  whiten- 
ing of  the  shell  membrane  exposed  around  the  edges  of  the  opening 
where  the  chick  has  pipped  the  shell  and  before  it  has  gotten  out.    As 


this  shell  membrane  dries  it  becomes  tough,  and  the  chick  is  unable 
to  tear  through  it  and  dies  in  its  efforts  to  get  out.  The  membrane 
should  remain  moist  while  the  chick  is  breaking  out  of  the  shell,  for 
it  is  then  soft  and  easily  torn. 

One  of  the  best  ways  to  supply  needed  moisture  when  using  a 
" non-moisture"  machine,  is  to  keep  the  floor  well  soaked.  The  evap- 
oration of  moisture  is  in  proportion  to  the  water  surface  exposed  to 
the  air,  so  that  wetting  down  the  floor  exposes  a  large  water  surface 
and  enables  the  air  to  become  well  saturated  before  entering  the  in- 
cubator. The  purpose  of  such  moisture  is  not  to  supply  it  to  the 
eggs,  but  to  keep  the  air  entering  the  incubator  moist  enough  not  to 
take  up  too  much  moisture  from  them  and  thus  rob  the  embryos  of  the 
water  they  absolutely  need  in  order  to  develop  into  strong,  lusty  chicks. 

Turning. — Turning  is  usually  begun  twenty-four  to  forty-eight 
hours  after  the  eggs  are  put  into  the  incubator  and  continued  morning 
and  night  until  the  first  egg  pips.  The  turning  periods  should  be  as 
near  twelve  hours  apart  as  possible.  Perhaps  the  easiest  and  best 
way  to  turn  is  to  use  a  rotary  motion,  rolling  the  eggs  slowly  with 
the  palms  of  the  hands.  They  will  not  break  even  if  considerable 
pressure  is  used,  provided  they  are  not  jarred  or  handled  with  sudden 
motions.  The  eggs  do  not  have  to  be  turned  completely  over.  All  that 
is  necessary  is  that  the  eggs  be  shifted  around  a  little  so  that  the 
embryos  will  not  stick  to  the  shells. 

Cooling. — The  purpose  of  cooling  is  to  thoroughly  air  the  eggs 
and  strengthen  the  embryos.  It  corresponds  to  the  opening  of  the 
windows  by  the  housewife  each  morning  to  air  the  bedroom.  The 
incubator  door  should  not  be  left  open  while  eggs  are  being  cooled. 
The  aim  is  to  cool  the  eggs,  not  the  incubator.  The  hen's  body  tem- 
perature is  the  same  when  she  returns  to  the  eggs  as  it  was  when  she 
left  them.    So  it  should  be  with  the  incubator. 

In  setting  the  eggs  out  to  cool  do  not  allow  any  part  of  the  tray 
to  project  beyond  the  table  or  incubator,  or  the  eggs  will  cool  unevenly 
and  those  in  the  projecting  part  of  the  tray  will  become  chilled  by  the 
time  the  others  are  ready  to  go  back  into  the  machine.  Begin  cooling 
on  the  seventh  day  and  cool  every  evening  when  the  eggs  are  turned. 
Cool  a  little  at  first  and  gradually  lengthen  the  cooling  period  as  the 
hatch  advances.  A  most  satisfactory  way  to  tell  when  the  eggs  are 
cooled  sufficiently  is  to  hold  the  small  ends  of  a  few  to  the  eye.  When 
they  feel  barely  warm  the  eggs  are  cooled  enough.  A  little  experience 
will  make  one  expert  in  gauging  the  cooling  period.  They  will  cool 
down  rapidly  at  first,  but  as  the  embryos  develop  and  contain  animal 


6 

heat  of  their  own  they  will  cool  down  more  slowly.  In  the  month  of 
May,  twenty  to  sixty  minutes  is  often  required  to  cool  eggs  that  have 
been  in  the  incubator  fourteen  to  eighteen  days.  The  amateur  usually 
errs  on  the  side  of  too  little,  rather  than  on  that  of  too  much  cooling. 
Testing.— Test  on  the  seventh  and  fourteenth  days,  at  night,  be- 
cause that  is  the  time  the  cooling  is  done.  The  first  test  will  remove 
all  infertile  eggs  and  dead  germ  eggs  up  to  that  period.  The  infertile 
eggs  are  still  perfectly  good  and  can  be  used  in  cakes.  The  writer 
has  known  them  to  be  so  used  and  considers  them  as  good  as  cold- 
storage  eggs  for  cooking  purposes.  The  dead  germs  at  the  seventh- 
day  test  contain  either  blood  clots  or  blood  rings.  Every  egg  in  which 
a  dark  movable  black  spot,  a  little  larger  than  a  pinhead,  with  numer- 
ous radiating  blood  vessels  is  not  distinctly  visible  should  be  discarded 
as  worthless.    Good,  strong  eggs  only  will  hatch  good,  vigorous  chicks. 


Dead  germ,  seventh  day 


Fertile  egg,  seventh  day 
Fig.  3 


Infertile  egg 


On  the  fourteenth  day  the  strong  eggs  will  be  opaque  and  nearly  black, 
and  if  such  an  egg  can  be  held  still  before  the  tester,  the  embryo  can 
be  seen  to  move.  Dead  germs  at  this  time  contain  either  blood  rings 
or  blood  streaks,  or  are  perfectly  translucent  and  cloudy. 

The  Hatch.— After  the  last  turning,  close  up  the  incubator  and 
do  not  disturb  it  again  until  the  hatch  is  over,  except  to  fill  the  lamp. 
As  soon  as  all  the  chicks  have  dried  off,  open  wide  the  ventilators, 
remove  the  egg  tray  and  all  the  eggshells,  and  wedge  open  the  door 
with  a  match  stick  so  as  to  harden  the  little  fellows,  but  do  not  let 
the  temperature  in  the  nursery  go  below  100  degrees  F.  Darken  the 
egg  chamber  by  hanging  a  cloth  in  front  of  the  glass  door  to  keep 
chicks  from  picking  at  the  droppings  and  at  each  other's  toes.  After 
twenty-four  hours  remove  them  to  the  brooder  in  a  flannel-lined  and 
hooded  basket.  A  chilling  draught  striking  them  at  this  time  would 
prove  disastrous. 


